Process for making strontium-bearing ferrosilicon



United States Patent 3,374,086 PROCESS FOR MAKING STRONTIUM-BEARING FERROSILICON Henry G. Goehring, Jr., Niagara Falls, N.Y., assignor to gnion Carbide Corporation, a corporation of New Olk No Drawing. Filed June 16, 1965, Ser. No. 464,581 2 Claims. (Cl. 7510) The present invention relates to the manufacture of a strontium-containing ferrosilicon alloy for use as an addition to cast iron. More particularly, the present invention relates to the manufacture of a strontium-containing ferrosilicon alloy having a very low calcium content.

In the making of ductile iron by treating cast iron with metal additions, i.e., innoculants, it is known that ferroalloys containing strontium are exceptionally eifective, but only when the calcium content is kept very low, e.g. on the order of 0.1%.

Difficulty has been encountered however in controlling the strontium-calcium contents in such alloys using previously 'known methods of manufacture. These methods involved the adding of a strontium-bearing mineral e.g. celestite to a bath of molten ferrosilicon, mixing the materials until equilibrium has been apparently achieved, and casting the resulting product.

With the use of techniques of this type, strontium and calcium contents are not always constant, and strontium recovery is relatively low. In addition, processes of this type are not always suited to large-scale operation in conventional production facilities due to the requirement of extensive mineral-metal mixing.

It is therefore an object of the present invention to provide a relatively simple process for producing ferrosilicon alloys having a controlled strontium-calcium content.

It is another object of the present invention to provide strontium-containing ferrosilicon alloys having a very low calcium content.

Other objects will be apparent from the following description and claims.

A particular embodiment of a process in accordance with the present invention comprises smelting in a submerged arc furnace a mixture of quartzite, celestite and carbonaceous reducing agent to provide a master alloy containing 15 to 55% strontium, 40 to 75% silicon, up to incidental impurities such as barium, iron, carbon, and having a calcium content not more than $4 the strontium content. The alloy thus obtained is then added to molten high purity ferrosilicon alloy (at least 98.5% Fe-l-Si, less than 0.05 Ca) in an amount to provide in the ferrosilicon a strontium content of from at least 0.5%, suitably 0.5 to 1%. Higher strontium contents up to 4% and higher can also be efficiently provided.

In practicing the present invention, the celestite employed in the charge contains at least 35% strontium and has a strontium to calcium ratio of at least 10 to l, and the amount of carbonaceous reducing agent is at least 90% of the stoichiometric amount required to reduce the strontium in the ore and the silicon in the quartzite to produce the desired alloy. Suitable ratios of celestite and quartzite to produce various alloys are shown in Table I.

TABLE I celestite-silica ratio: Alloy, percent Sr 0.90 30 to 55 0.35 Up to 30 By following the present invention, several important advantages are obtained. For example, reduction of calcium in the celestite to metal is depressed to the extent that a strontium to calcium ratio of at least 10 is achieved in the master alloy. Moreover, very constant strontiumcalcium ratios are obtained. Additionally, high recoveries ice of strontium, 85% and higher, are achieved upon the addition of the master alloy to molten ferrosilicon.

. The following example will further illustrate a preferred embodiment of the present invention.

Example I A furnace mix blend for a 45% Sr strontium-silicon alloy was prepared as follows:

Percent Sr=43.78.

Percent Ca=1.97.

The mix was charged to an electric furnace lined with quartzite to a 21 inch diameter. An 8 inch diameter graphite electrode was used in submerged arc operation at an electrode to hearth voltage of volts and a load of 450 kw.

Furnace operation was satisfactory and the intermediate alloy product was tapped without difiiculty. More than 4000 pounds of alloy were ultimately produced analyzing from 43.2 to 47.2% strontium and from 2.20 to 2.96% calcium.

A master alloy produced as above, sized 2 inches by down, was stirred into Si high purity ferrosilicon (98.5% Fe-l-Si, less than 0.05% Ca) to obtain a final alloy containing about 1% Sr. The required amount of master alloy can be dissolved in 1800 lbs. of 75 ferrosilicon in less than 5 minutes. The temperature of the ferrosilicon at the time of addition was about 2750 and a temperature loss of l25175 F. is experienced due to this alloy addition. Average analysis of the final alloy obtained was as follows:

Alloy Percent Si 72 Sr 0.9 Ca 0.076

Strontium recovery was approximately What is claimed is:

1. A process for producing strontium-containing ferrosilicon having a low calcium content which comprises smelting in a submerged arc furnace a mixture of quartzite, celestite and carbonaceous reducing agent to provide an alloy containing 15 to 55% strontium and 40 to 75 silicon, the strontium to calcium ratio in the celestite being at least 10:1; and subsequently adding the aforesaid alloy to molten ferrosilicon containing at least 98.5% Fe-l-Si, the amount of alloy added being sufficient to provide a strontium content of at least 0.5%.

2. A process for producing strontium-containing ferrosilicon having a low calcium content which comprises smelting in a submerged arc furnace a mixture of quartzite, celestite and carbonaceous reducing agent to provide an alloy containing about 45% strontium and about 50% silicon, the mixture being in the proportions of about 200'parts quartzite, 152 parts celestite, 46 parts charcoal, 120-parts'wo0d chips" and 96' parts coal, the strontium to calcium ratio in the celestite being at least 20 to 1; and subsequently adding the aforesaid alloy to molten ferrosilicon', at a temperature-of ab0ut'2750" F said ferrosilicon containing at least 985% Fe+Si, theamount of alloy added'being sufiicient to provide a strontium content of about 1%.

References Cited UNITED STATES PATENTS 3,333,954 8/1967 Dawson 75--129 DAVID L. RECK, Primary Examiner.

H. M. TAR-RING, Assistant Examiner. 

1. A PROCESS FOR PRODUCING STRONTIUM-CONTAINING FERROSILICON HAVING A LOW CALCIUM CONTENT WHICH COMPRISES SMELTING IN A SUBMERGED ARC FURNACE A MIXTURE OF QUARETZITE, CELESTITE AND CARBONACEOUS REDUCING AGENT TO PROVIDE AN ALLOY CONTAINING 15 TO 55% STRONTIUM AND 40 TO 75% SILICON, THE STRONTIUM TO CALCIUM RATIO IN THE CELESTITE BEING AT LEAST 10:1; AND SUBSEQUENTLY ADDING THE AFORESAID ALLOY TO MOLTEN FERROSILICON CONTAINING AT LEAST 98.5% FE+SI, THE AMOUNT OF ALLOY ADDED BEING SUFFICIENT TO PROVIDE A STRONTIUM CONTENT OF AT LEAST 0.5% 